Background: Twin to twin transfusion syndrome (TTTS) affects around 15% of
monochorionic diamniotic twin pregnancies (MCDA). Left untreated, mortality/serious
morbidity approaches 100%. Antenatal intervention with serial amnioreduction or laser
ablation of communicating vessels has been shown to improve outcome with survival rates of
50-69%. However, significant rates of morbidity are seen in survivors with neurodisability
rates of 25% following amnioreduction and 5-11% following laser ablation.

Purpose of study: To ascertain regional outcomes for pregnancies affected by (TTTS).

Methods: Two retrospective reviews of pregnancies affected by TTTS referred to the Wessex
Fetal Medicine Service between 1997-2001 and 2002-5 and were undertaken in accordance
with UK ethical guidelines. During time period 1 serial amnioreduction was the only treatment
offered but in period 2 early TTTS (stage1 and 2) was treated with amnioreduction and more
severe or non-responsive disease being referred for laser ablation. Patients were identified via
the fetal medicine database and data collated by a combination of note and database review.

Results: Overall 56 pregnancies were affected by TTTS. In period 2 this represented 19.8% of
all MCDA pregnancies. 62% of cases were diagnosed before 20 weeks. In period 1 one patient
received laser treatment whilst in the second period 33% received laser treatment +/-
amnioreduction. Average age at delivery was 29.8 weeks but where both twins survived
average gestation was 32.9 weeks and where neither twin survived 23.5 weeks. 69% were
liveborn (64%/77%) with overall survival rates of 53% and 58%. Of babies dying in the
neonatal period the average gestation at delivery was 26 weeks and average birthweight 586g.

As expected significant morbidity was seen in liveborn infants. Over 50% showed evidence of
renal impairment half of which was severe. During period 1 8.7% of infants required dialysis
and one infant is likely to develop end stage renal failure in childhood. No babies required
dialysis in the second cohort. There were high rates of early echocardiographic abnormalities
and 15% of survivors showed significant ventricular hypertrophy or tricuspid regurgitation and
20% significant hypertension. Ischaemic complications were not uncommon with 7.5%
developing necrotising enterocolitis and 9.3% affected by limb ischaemia including antenatal
ischaemic below knee amputation.

Ultrasound changes suggestive of cerebral ischaemia were seen in 14.8% with the development
of cystic periventricular leukomalacia in 8.7%. Only one infant has been identified as having
cerebral palsy on follow up (2%) but ascertainment is not complete.

Conclusion: Survival rates for infants are comparable with published data. TTTS is associated
with significant mortality and morbidity. Neurological morbidity is well recognised but other
organ damage can also be associated with poor outcome.